This application is based on Application No. 2001-157745, filed in Japan on May 25, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a vehicle surroundings monitoring device that is mounted on a vehicle and monitors the surroundings of the vehicle, and more particularly to a vehicle surroundings monitoring device that calls an alarm to a drive in order to prevent a contact and collision with an obstacle at the time of changing a lane or the like.
2. Description of the Related Art
The inventors of the present invention have already filed an application of a vehicle surroundings monitoring device mounted inside the vehicle door mirror of this kind in Japanese Patent Application No. Hei 11-325688. This vehicle surroundings monitoring device has a transmitting circuit for generating waves to be transmitted, an antenna capable of radiating transmitted waves through a mirror surface of the door mirror, and a receiving circuit for receiving, by the antenna, reflected waves from an object existing near the vehicle, the reflected waves propagating to the antenna through the mirror surface of the door mirror. This vehicle surroundings monitoring device have a reflective film which is formed on the mirror surface of the door mirror by vapor deposition and reflects light of wavelengths in the visible region but allows electric waves of several gigahertz to pass therethrough, and is designed to detect an obstacle behind the vehicle.
Even in the case where a reflective film through which electromagnetic waves can be transmitted are vapor-deposited on a mirror surface of a door mirror as in the above described conventional vehicle surroundings monitoring device, a reflection from a mirror base surface and a reflection due to the reflective film also occur to some extent. For the above reason, electric waves radiated from a transmission antenna are radiated toward not only a back side of a vehicle that travels on a center lane portion but also toward a front side thereof as shown in FIG. 7. For that reason, in the case where electric waves radiated forward of the vehicle are present, since a vehicle running in front of the vehicle is also detected, there arises such a problem in that it is difficult to distinguish between an obstacle in front of the vehicle and an obstacle in the rear thereof.
Also, the reflected waves from the above reflective film are irregularly reflected in the interior of a housing and stray into a receiving antenna. The level of straying of the reflected waves greatly varies according to the relative positions of the mirror base material, the reflective film, the antenna and the housing. In the case where the straying level of the reflected waves has changed significantly, when an obstacle actually exists at a short distance from the vehicle, the obstacle cannot be detected depending on the distance resolution of a radar, or the distance measuring performance is adversely affected by the fluctuation, whereby the possibility of an alarm failure or a false error becomes high.
The present invention has been made in order to solve the above problem, and therefore an object of the present invention is to provide a vehicle surroundings monitoring device, which is capable of surely detecting an obstacle at the rear of a vehicle without such a detection error that the obstacle in front of the vehicle is detected, by shielding electric waves reflected by a door mirror surface and radiated toward the front of the vehicle.
Also, another object of the present invention is to provide a vehicle surroundings monitoring device, which is capable of supplying accurate alarm information to a driver without deteriorating the distance measuring performance over a short distance by reducing irregular reflection within a housing.
In order to achieve the above objects, according to the present invention, there is provided a vehicle surroundings monitoring device which monitors surroundings of a vehicle, the device comprising: a transmitting antenna which is mounted in the interior of a door mirror of the vehicle and radiates transmitted waves through the surface of the door mirror; and a receiving antenna that receives reflective waves from an object existing near the vehicle through the surface of the door mirror, wherein an electric wave blocking structure which blocks unnecessary electric waves radiating toward the front of the vehicle is provided to a housing of the door mirror and the supporting portion which supports the mirror surface of the door mirror and has the transmitting antenna and the receiving antenna built therein.
In a preferred form of the present invention, the housing and the support portion per se are formed from an electromagnetic shielding material as the electric wave blocking structure.
In another preferred form of the present invention, the electromagnetic shielding material is arranged on an inner surface of the housing and an inner surface of the support portion as the electric wave blocking structure.
In a further preferred form of the present invention, an electric wave absorber is arranged on an inner surface of the housing and an inner surface of the support portion as the electric wave blocking structure.